In general, a wavelength conversion phosphor material is used to convert a certain wavelength of light from various light sources into a desired wavelength of light. In particular, a light emitting diode (LED), among various light sources, is able to be driven with low power consumption and has excellent light efficiency, so it may be effectively applied to an LCD backlight, a vehicle lighting system, and a home illumination system. Recently, a phosphor material has been recognized as a core technology in the manufacturing of a white light emitting device (LED).
The white light emitting device is generally manufactured using a scheme of covering a blue LED with a yellow phosphor. In detail, white light may be produced by covering a light emission surface of a blue LED having a GaN/InGaN active layer with a yellow YAG(Y3Al5O12):Ce phosphor to convert a certain amount of blue light into a yellow light, such that the converted yellow light and non-wavelength converted blue light may be combined to thereby provide white light.
The white light emitting device configured with the above-mentioned YAG:Ce phosphor (or, TAG-based phosphor)-blue LED according to the related art has low color rendering. That is, since a wavelength of the white light produced using the yellow phosphor is distributed in only blue and yellow colors, the color rendering is relatively low, and thus, there is a limitation in implementing desired natural white light.
Meanwhile, a wavelength conversion phosphor material according to the related art has been used in a limited fashion in a light emission color of a particular light source and color of a particular output light, and a color distribution able to be implemented is also very limited, such that there are limitations in the application thereof to light emission colors of various light sources and/or the colors of various output light.
With regard to the defects described above, an excellent color rendering index (CRI) and a relatively high color distribution have recently been implemented through a mixture of three kinds of particular blue, green and red phosphors through the disclosure of Korean Patent Application No. 2004-0076300 (Filed Sep. 23, 2004). In order to implement an excellent light emitting device through the composition of red, green and blue phosphors, respective phosphors are all required to have relatively high conversion efficiency.
In addition, a silicate phosphor according to the related art is unstable when heated, such that it is vulnerable to failure when used in conjunction with a high-output LED chip.
In the case of defects, research into a β-sialon phosphor has been continuously conducted since the initial proposal for a new phosphor material was disclosed in Japanese Patent Laid-Open Publication 60-206889 (Published Oct. 18, 1985).
Japanese Patent Registration No. 3921545 (Published Mar. 2, 2007, Patentee: National Institute for Materials Science) proposes using β-sialon as a green light emitting phosphor, but there are difficulties in practical implementation, because the brightness thereof is very low and wavelength and color coordinate characteristics are not appropriate to implement a desired white light.
Meanwhile, a scheme for finding new properties of a β-sialon phosphor by transforming a basic crystal structure thereof has been reported. A thesis, “Fluorescence of Eu+ in SiAlONs” (2005, Journal of the Ceramic Society of Japan, R. J. Xie, et al.) proposes a strontium (Sr) sialon provided by substituting Sr in place of Si or Al in the crystal structure. However, since Sr is substituted in the crystal structure, phase stability is relatively low and it is difficult to expect thermal stability.
In addition, Korean Patent Laid-Open Publication 2009-0028724 proposes β-sialon (SiAlON) as a green phosphor, but since there are disadvantages in which a particle size is relatively large, precipitation speed is rapid and dispersion of color coordinates based on the kind of product is relative large. Further, in a manufacturing process, a high firing temperature, for example, 2000° C. or more, and a long firing time in comparison with the firing condition of a silicate phosphor according to the related art, for example, a temperature of about 1600° C. and about 3 hours may be required. Due to these disadvantages, difficulties in adding group I and II elements as an active agent may be caused.